Several approaches were taught in the prior art to produce single and multiple colored luminescent images for applications in security printing, laser marking, anti-counterfeiting, automatic identification and digital imaging. For example, U.S. Pat. Nos. 5,755,860 and 5,837,042 taught the use of inkjet printing process for application in anti-counterfeiting. This printing process uses invisible ink compositions containing fluorescent colorants to produce luminescent images.
U.S. patent application Ser. No. 2002/0079249 disclosed a method and apparatus employing multi-spectra images for the remote identification and sorting of objects. The luminescent compositions contain fluorescent dyes or pigments, which were applied onto substrate by different printing and heat-sealing processes.
PCT application WO 02/04223 disclosed the injection molding of plastic compositions containing a luminescent compound, which irreversibly changes to non-luminescence upon exposure to laser radiation. Such compositions do not exhibit multiple luminescent color changes and require high radiation energy to encode the information or marking.
Research has also been done on fluorescent resonance energy transfer (FRET) between some conjugated blue emitting polymers and rare-earth metal complexes, to achieve a pure red emission for example, which is known to be difficult to obtain1. A control of such an energy transfer on precise locations on a polymeric film would possibly lead to a patterned Red-Blue-Green (RBG) emission on a single-layer emitting device2.
However, the prior art fails to disclose methods for recording information in luminescent compositions by simple exposure to a photon source under ambient conditions.
Thus remains a need for such methods for recording information in luminescent compositions by simple exposure to a photon source under ambient conditions.
The present invention seeks to meet this and other needs.